This distinction matters because some deviations announce themselves — a participant who does not show up for a visit, a pharmacy that cannot dispense the study drug — and some do not. The quiet deviations are the dangerous ones. A blood draw performed ten minutes after the protocol window closes. A vital sign measurement taken with the participant standing when the protocol specifies seated. A concomitant medication started between visits that the participant forgot to mention. These events do not trigger alarms. They do not generate error messages. They slip past unless the coordinator is actively watching for them.

And the timing of identification matters too. A deviation recognized in real time — as it occurs — creates the opportunity for immediate corrective action. The coordinator who notices that the pre-dose PK draw window is about to close can sometimes prevent the deviation entirely. A deviation discovered retrospectively — during data review, monitoring preparation, or audit — can only be documented and analyzed. The event has already happened. The question then is not "can we prevent this?" but "did this affect the participant or the data?"

This lesson teaches both modes of identification: the real-time awareness that prevents or catches deviations during visits, and the systematic retrospective review that finds the ones that were missed.

This distinction matters because some deviations announce themselves — a participant who does not show up for a visit, a pharmacy that cannot dispense the study drug — and some do not. The quiet deviations are the dangerous ones. A blood draw performed ten minutes after the protocol window closes. A vital sign measurement taken with the participant standing when the protocol specifies seated. A concomitant medication started between visits that the participant forgot to mention. These events do not trigger alarms. They do not generate error messages. They slip past unless the coordinator is actively watching for them.

And the timing of identification matters too. A deviation recognized in real time — as it occurs — creates the opportunity for immediate corrective action. The coordinator who notices that the pre-dose PK draw window is about to close can sometimes prevent the deviation entirely. A deviation discovered retrospectively — during data review, monitoring preparation, or audit — can only be documented and analyzed. The event has already happened. The question then is not "can we prevent this?" but "did this affect the participant or the data?"

This lesson teaches both modes of identification: the real-time awareness that prevents or catches deviations during visits, and the systematic retrospective review that finds the ones that were missed.